#501″FQDN” is invalid or DNS says does not exist

Undeliverable: destinationdomain.com rejected your message to the following e-mail addresses:

Recipient (recipient@destinationdomain.com)

destinationdomain.com gave this error:<EX01.doitfixit.local> is invalid or DNS says does not exist A problem occurred during the delivery of this message to this e-mail address. Try sending this message again. If the problem continues, please contact your helpdesk.

Diagnostic information for administrators:

Generating server: EX01.doitfixit.local

recipient@destinationdomain.comdestinationdomain.com #501 <EX01.doitfixit.local> is invalid or DNS says does not exist ##